1. Field of the Invention
The present invention relates to a method for recovering uranium and plutonium from solid raw wastes, especially from fabrication shops for nuclear fuels, and to the processing of the wastes freed of uranium and plutonium into a space-saving product that can be committed to ultimate storage.
2. Background of the Invention
The degree of contamination of these voluminous wastes which accumulate within the scope of control of a manufacturing operation differs greatly. Wastes with weighable, that is stronger, contamination by fission materials such as uranium and plutonium are produced almost exclusively in the glove boxes and amount to approximately one-half of the total wastes. As far as the material is concerned this waste contains PVC (polyvinyl-chloride), rubber, polystyrene (PS), polymethylmethacrylate (PMMA), polyethylene (PE), polytetrafluoroethylene (PTFE) and others. In addition to these plastics, cellulose and other burnable natural substances are also found in the waste material. Quantitatively, the PVC with a content of up to 70% by weight predominates in this mixture.
These wastes cannot be removed in the conventional manner, since they contain long-life radiotoxic fission materials (plutonium). In order to achieve ultimate storage of the wastes without danger, the objective of new treatment processes is the recovery of the fission materials, a reduction of the primary waste volume and the generation of a waste product that can be committed to ultimate storage.
Up to now one has confined oneself in practice to locking such wastes in cement blocks in order to obtain the lowest possible leaching rate vis-a-vis water or salt solutions and to store them ultimately in salt mines. It is a disadvantage of this method that the waste volume is expanded considerably and a recovery of plutonium at a later time is no longer possible.
To eliminate these disadvantages, a number of combustion methods has been developed primarily in the U.S.A., in which a concentration of the fission material to a small residual volume, the ash content was to be achieved. As can be seen from the survey report KfK-2250 of the Nuclear Research Center in Karlsruhe, no method has been able to attain production maturity, due to unresolved difficulties.
It is a common disadvantage of all combustion methods that, in the case of the mentioned wastes with a high PVC content, the contaminated secondary waste quantity in the fixed form ready for ultimate storage exceeds the starting volume of the primary wastes. In some high-temperature processes it is an additional aggravation that the plutonium, during the combustion, is converted into a very-hard-to-dissolve form, which makes recovery from the ash considerably more difficult.
Since up to now no method is known by which fission material recycling and at the same time a reduction of the volume are achieved, the problem arose to find a path for reaching the stated goal.